Film-Tech Forum ARCHIVE: CP65 BluRay Dolby Level

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Posted by Richard May (Member # 2627) on 09-11-2013, 11:10 AM:

When we ran DigiBeta here, there was always tone and color bars on the head of the tape. We ran left and right output to the Non Sync inputs and had the jumpers set to 2:4 so we could get sound out of everything. It worked great because you can use the cat 222 to set dolby level. Now that we run BluRay instead of Digi, there never is tone to adjust level. Is there a way to send tone into the inputs to set it?

Posted by Carsten Kurz (Member # 5396) on 09-11-2013, 06:57 PM:

How do you feed the BluRay audio to the CP65? NonSync, ext 6ch?

BluRay does not have an explicit reference audio level, nor do the analog outputs of common BluRay Players. You can only set your own reference after having shown a few discs.

- Carsten

Posted by Richard May (Member # 2627) on 09-11-2013, 07:21 PM:

I guess it's a little complicated. We sometimes get discs that are LT/RT which we run through Non Sync. The problem is that the recorded levels on the discs are SOOOO different from disc to disc. Sometimes it's recorded so high that the Cat222 is pinned on both channels throughout the entire movie. Of course it's all distorted no matter how low I bring the pots down. My thought was to see if there was a basic reference level to set the Cat 242 pots to. This way we can tell if a specific DVD or BD was recorded higher or lower. There are many 1K tone files out there that I can burn to a disc and play back to set level but at what level should it be on the disc? 0db, -10db,etc.... It would also keeps the channels balanced from LT to Rt.

Posted by Scott Norwood (Member # 30) on 09-11-2013, 07:32 PM:

Not sure about Blu-Ray, but, with the tape formats, the reference tones are typically at either -20dBFS or -12dBFS, with -20 being more common.

Realistically, though, video sound is all over the map, since most of this stuff (and especially the home-made disks) is not mixed for theatrical playback. I usually set things up by ear so that "normal" content plays somewhere between 6-7 on the fader and let the operator adjust for anything weird.

Alternatively, you could use a DMA8 (plus) to feed the digital output of the BR player into the external 6-channel input on the CP65, in which case 7.0 would be your reference level.

Posted by John Wilson (Member # 269) on 09-11-2013, 07:41 PM:

quote: Scott Norwood
Realistically, though, video sound is all over the map, since most of this stuff (and especially the home-made disks) is not mixed for theatrical playback. I usually set things up by ear so that "normal" content plays somewhere between 6-7 on the fader and let the operator adjust for anything weird.

All audio levels are all over the shop...no matter whetehr they are 'home made' movies or from the majors studios. For example, this week I'm playing RIDDICK at 6.5, BLUE JASMINE on 5.5 and RIPD on 4.0.

You just need to test screen prior and set the level then. There is no standard.

Posted by Richard May (Member # 2627) on 09-11-2013, 07:59 PM:

I know there is no standard even though every film maker that comes in with a DVD says "the level was mixed to industry standards". One of my concerns is cranking the 242 pots to max on certain DVD's that are so low. Can you overdrive what's after those pots?

Posted by Brad Miller (Member # 2) on 09-11-2013, 10:24 PM:

Check your EQ John. I find it is rare to deviate from 7, and even then it's usually just 1/2 point. I have consistently when the room has acoustical issues or the sound system is not properly calibrated that the room is far more sensitive to needing sound adjustments.

Posted by Steve Guttag (Member # 268) on 09-12-2013, 09:48 AM:

Funny you should mention this. I have a set of discs (DVE by Joe Kane) that do indeed have reference tones and noise. The tones (440Hz) are -20dBFS. I set up the system using these and since this was going into an A/V DSP system, I made sure the meters were spot on to avoid digital clipping on the input side.

The system used an HDMI decoder for the various formats (Dolby True HD, DTS Master audio, LPCM...tc). After setting it up, I ran some tests using some high-power tracks like "Saving Private Ryan" and sure enough...the levels got high but never quite clipped (came close).

I then ran a BluRay with DTS Master Audio encoding...it clipped ("Walk The Line"). Now -20dBFS is just that...there shouldn't be any way for it to go higher than 0dB...that is Full Scale...digitally it couldn't...which means that on the decoder side, it outputs DTS at a higher level...WTF? Through some experimenting...I determined it was about a 10dB difference between DTS and everything else.

Posted by Richard May (Member # 2627) on 09-12-2013, 02:01 PM:

I recorded two discs. One with 1K Tone -10db and the other -20db. The -20db running through Non Sync inputs gets me double green on the Cat 222 at around 11 turns of the pot which is slightly more than halfway. Sounds like a good start.

Posted by Carsten Kurz (Member # 5396) on 09-13-2013, 06:46 AM:

If you interface through analog, you should simply add a basic mixer in between so you can adjust levels on it. It's not a good idea to do it on the CAT222 for every other disc.

You also have to consider that stereo is not the only option. If there is only a stereo track on the disc, overall level will probably be lower than if there is a 5.1 track being downmixed into 2ch. You simply can not rely on any reference level there.

What player do you use?

- Carsten

Posted by Richard May (Member # 2627) on 09-13-2013, 04:45 PM:

If your concern is damaging the pots on the 242 card, I've been doing it without a problem for about 10 years. A mixer before the inputs is a good idea though. We do it that way during festivals.
We use an OPPO BDP93. When the disc is 5.1 we go into the CP65 digital inputs. When a disc is only marked stereo, we also go in through the digital inputs (L&R only). Only when a disc is marked LT/RT do we go through the Non Sync inputs.

Posted by Jarod Reddig (Member # 6363) on 09-14-2013, 10:19 PM:

Do as Steve said. I too have HD Basics:Digital Video Essentials (DVE) by Joe Kane and i use it to set my levels in my home cinema. Its right in the ballpark. Id give it a try. Great test patterns on there too.